In this continuing collaboration with NIAMS researchers (Drs. K. Wang, J.G. Forbes and K. Ma), atomic force microscopy (AFM) and related bioengineering and physical science methods are being applied to investigate muscle protein biophysics and physiology/pathologies. On the foundation of our earlier work that included AFM structural imaging and force response characterization of AdhE enzyme and Calmodulin, we have proceeded further on investigating the behaviour of the large muscle proteins titin (a massive peptide chain of 3-4 MDa) and nebulin (600-900 kDa). Systematic AFM measurements with extensive data interpretation effort, as presented in a comprehensive review we have published, are being focused on understanding the elasticity of the PEVK motif of titin in its environment. The resulting insights have now been expanded by parallel circular dichroism studies that lead us to propose titin PEVK as a highly evolved nanoscopic gel-like enthalpic spring, in contrast to a simple commonly assumed entropic spring. The crucial functions of titin in maintaining skeletal and cardiac muscle organization and force responses, as well as the natural of nebulin protein, remain to be of high research interest.